High-velocity primary air nozzle



March 28, 1961 c. ALLANDER ETAL 2,976,794

- HIGH-VELOCITY PRIMARY AIR NOZZLE Filed April 25, 1958 FIELI.

INVENTORSZ CLAES ALLANDER BIRGER LARKFELDT ATTYS.

HIGH-VELOCITY PRIMARY AIR NOZZLE Claes Allander, Sodra Angby, and BirgerLiirkfeldt, Jonkoping, Sweden, assignors to Aktiebolaget SvenskaFlaktfabriken, Kungsgatan, Stockholm, Sweden Filed Apr. 25, 1958, Ser.No. 731,045 Claims priority, application Sweden Apr. 30, 1957 3 Claims.(CI. 98-38) The present invention relates to a device for inducing andmixing by ejecting action secondary air into a current of primaryair-discharged from a duct or pressure chamber, said device consistingof nozzle means connected to said duct or chamber.

Devices of this kind are nowadays used for ventilating plants in orderto create a circulation of the room air by means of a limited preferablypre-treated quantity of air supplied to said room. It can be madeevident both theoretically and experimentally, that when a resistance ispresent for the flow of the mixture, the quantity of secondary airincreases with increasing velocity of the discharged primary air andwith an increased value of the total boundary lines of the primary-airjets. Since in actual practice it is desired to have a heavy ejection ofroom air and an intimate mixing between primary and secondary air, itwill be necessary to work with as high a discharge velocity as possibleand with as large a value of the total boundary lines of the primary airjets as possible.

A problem which arises when air is given high velocities is that noiseoccurs. In apparatus of the kind used Within the ventilatingtechnique-to which the present invention relatesthere is anextraordinary requirement for freedom from noise. The noise occursusually because of whirling currents and increases with the extent ofwhirls and these usually arise in the nozzles or flow passagesconstituting the discharge means for the primary air.

The deciding factor for the degree of the occurrence of whirls in a flowpassage for a medium is the actual Reynolds number for the flow. Thisnumber is defined as the product of the how velocity of the medium andthe hydraulic diameter of said flow passage divided by the kineticviscosity of the flowing medium. In a long channel a shifting fromlaminar to turbulent flow occurs at a value of the Reynolds number ofabout 2000. As the length of the flow passage decreases said valuedecreases depending upon disturbances in the inlet of said passage. Whenthe flow is laminar hardly any noise occurs, and thus the most silientpressure reduction can be obtained in this kind of flow. The rule maythus be so formulated that for a constant pressure reduction, the noiseincreases with increasing Reynolds number, and thus a method to satisfythe requirement for noise elimination is to work with small Reynoldsnumbers. In order to obtain the necessary throttling or pressurereduction, the length of the passage must increase with a decrease inthe Reynolds number and thus the length of said flow passage inaccordance with the invention should considerably exceed the hydraulicdiameter of same.

The device according to the invention is constructed in accordance withthe above mentioned principles, and is characterized in that the primaryair nozzle means is provided with a great number of narrow slotsarranged mutually parallel and adjacent each other. The slots constitutethroats of a corresponding number of passages having substantially thesame cross-section area as 5' nited States Patent 0 said slots and beingso dimensioned with respect to their length as well as theircross-section area that the flow through said passages takes placewithout any obvious occurrence of whirls. The nozzle means shouldpreferably be made with a relatively small width in relation to thelength of same and the flow passages should be arranged substantiallyperpendicular to the longitudinal direction of the nozzle means. Withrespect to the actual medium velocity, the flow passages should be givensuch a hydraulic diameter that the Reynolds number does not exceed 2000.In order to eliminate as much as possible disturbing noises, the nozzlemeans should be made of a soft, sound-deadening material for instance ofrubber, plastic material or the like.

The invention will now be described more in detail with reference to theaccompanying drawing, wherein Fig. 2 is a cross-section along the line2-2 of Fig. 1.'

Fig. 3 is an elevational View in a larger scale with portions brokenaway illustrating the nozzle means applied to a duct.

Fig. 4 is an enlarged cross-section along the line 44 of Fig. 3 and Fig.5 is a horizontal plan view of the duct of Fig. 3.

In the drawing, a nozzle means 1 in accordance with the invention ismounted in a ventilating unit 3 and is connected to a duct 2, supplyingsaid unit with ventilating air (primary air). The unit in theillustrated embodiment of the invention is provided with a conventionalheat exchanger 4 for finally heating the air, inlet openings 6, 7 forsecondary air and a discharge opening 5 for the mixture of primary andsecondary air. The location of said openings 6 and 7 may be varied inaccordance with the placing of the unit. It is essential that the roomair introduced through said openings is conducted in such a way that theroom air will be supplied adjacent the nozzle means as shown by thearrows in Fig. 2. The nozzle means 1, according to the invention,comprises a generally rectangular hollow frame with a relatively smallwidth B in relation to its length L and provided with a great number ofspaced parallel narrow partitions disposed transversely of said frameacross its full width and defining a like number of narrow mutuallyparallel slots 8 arranged adjacent each other. Said slots constitute thethroats of a corresponding number of flow passages 9 havingsubstantially the same cross-sectional area as said slots. The flowpassages are connected at their inner ends to the conduit or duct 2 andare of uniform cross section throughout. At their outer ends, the flowpassages terminate in spaced parallel outlet openings or slots whichcreate a like number of flat streams of primary air flowing into theunit 3. The partitions between the multiplied by the velocity of theprimary air and divided by the kinetic viscosity of the air, produces aReynolds number below 2,000. In addition, the depth of the frame andpartitions should be substantially greater than the hydraulic diameterof the flow passages to reduce the effect of disturbances at the inletto the flow passages. The discharge slots 8 should, as in theillustrated embodi- 3 Es i ment be arranged substantially perpendicularto the length direction of the nozzle means in order to secure as largean area of introduction for the secondary air as possible. For the samereason the flow passages 9 are located-res shown in Fig. --with asuitable spacing with respect to their width X.

What we claim is: a

1. In an air conditioning room unit having a conduit for the supply ofhigh-velocity primary air, means to admit secondary room air into saidunit, and means to exhaust a mixture of primary and secondary air fromsaid unit; an elongated nozzle element within said unit comprising agenerally rectangular hollow frame connected at its inner end to theconduit and having a substantially plane outer surface, and a pluralityof spaced parallel narrow partitions disposed transversely of said frameacross its full width and coextensive in depth with said frame, saidpartitions defining'a plurality of transverse spaced parallel narrowflow-passages connected at their inner ends to said conduit, extendingthrough said frame with uniform cross section throughout and terminatingat their outer end in a like number of spaced parallel outlet openingscreating a like number of fiat streams 'of primary air flowing into saidunit, said partitions creating cavities of sub-atmospheric pressurebetween said streams into which the secondary air is drawn and mixedwith said primary air, the partitions being spaced apart relative to thewidth of said hollow frame to pro duce in said passages a hydraulicdiameter considerably less than the depth of the frame, and whenmultiplied by the velocity of the primary air flowing therethrough anddivided by the kinetic viscosity of the air producing a Reynolds numberbelow 2,000, whereby the flow through said passage is laminar withoutreducing the velocity of primary and thereby the quantity of secondaryair drawn into and mixed with said primary air in said unit.

2. A device according to claim 1 wherein the nozzle element isrelatively small in width in relation to its length and that the flowpassages are arranged substanperpendicular to the longitudinal directionof said nozzle means.

3. A device according to claim 1 wherein said primary air conduitextends through said unit and said nozzle element is disposedlongitudinally of said conduit whereby said narrow flow passages aredisposed transversely of the primary air flow in said conduit.

References Cited in the file of this patent UNITED STATES PATENTS1,463,263 Grayson July 31, 1923 2,161,027 Dollinger June 6, 19392,210,023 Candor Aug. 6, 1940 2,731,104 Baker Ian. 17, 1956 2,737,875Kurth Mar. 13, 1956 2,775,188 Cannon Dec. 25, 1956 2,835,187 Schell May20, 1958 2,872,859 Kennedy Feb. 10, 1959 FOREIGN PATENTS 530,178 GreatBritain Dec. 6, 1940 130,046 Sweden Nov. 7, 1950 1,140,710 France Mar.4, 1957

